Vapor coating aluminum on ironcontaining substrate



Oct. 7, 1969 c. M. OUALLINE, JR., ETAL 3,471,321

VAPOR COTING ALUMINUM ON IRON CONTAINING SUBSTRATE Filed Dec. 30, 1964ATTORNEY United States Patent O U.S. Cl. 117-102 4 Claims ABSTRACT F THEDISCLOSURE Disclosed are methods and apparatus for coating a metallicmember with a film of a different metal without the formation of anundesirable alloy or compound layer intermediate the metallic member andthe metal film. The method disclosed is a vapor phase process comprisingthe formation of a metal subhalide vapor by reacting a metal halidecompound with elemental metal of the same kind as the metal of the metalhalide compound, conducting the subhalide vapor while at a temperatureof no less than about 700 C. to 800 C. into Contact with the metallicmember to be coated while maintaining the temperature of the member at avalue below the melting point of the elemental metal to thereby deposita substantially pure film of the elemental metal on the member, andremoving the member from contact with the subhalide vapor while thetemperature of the member is maintained below the melting point of themetal. The member to be coated may be, for example, copper, tantalum,tungsten, niobium, molybdenum, nickel, platinum, paladium, silver, gold,titanium, iron, steel, chromium and mixtures and alloys thereof. Themetal film may be for example, aluminum, titanium, chromium, nickel,manganese, germanium and cobalt. Disclosed also is an apparatus forcoating the member which comprises a reaction chamber, an outer casingsurrounding said reaction chamber and defining cavities at opposite endsof said reaction chamber, means for the introduction of reactant vaporinto said reaction chamber, means for evacuating said cavities tomaintain subatmospheric pressure in said reaction chamber and saidcavities, and means for moving said metallic member through saidreaction chamber.

This invention relates to methods and apparatus for the coating ofmetallic surfaces.

In many instances it is desired to produce a thin coating of metal overa dissimilar metallic surface, for example, to produce a thin coating orfilm of a metal on a wire or strip made of a dissimilar metal.

The coating of a wire of one metal with a different type of metal ismost commonly accomplishedby drawing `the wire through a bath of themolten coating metal. Another method, applicable in certain instances,is the electrophoretic deposition of powdered aluminum around wire withsubsequent compaction. Still another method is based on compacting linemetallic powder around the wire and heating.

The foregoing methods have varying degrees of applicability, dependingon the dissimilar metals involved and depending on the particular degreeof metal film purity and other characteristics required for the ultimatecoated product.

T o facilitate consideration of certain specific problems 3,471,321Patented Oct. 7, 1969 lCC presented by the prior art methods, considerthe coating of an iron or steel wire with aluminum. If the aluminumcoating is applied by passing the iron or steel wire through a moltenbath of aluminum, it is found that the high temperature contact betweenthe liquid aluminum and iron causes the formation of an iron-aluminumintermetallic compound or of an alloy, in general, this intermetalliccompound is brittle and the coated wire consequently has physicallimitation imposed upon it by the brittle regions present in thestructure. Moreover, in quite thin films the intermetallic iron-aluminumcompound extends into the outermost regions of the coating and militatesagainst a high purity outer metal film. To eliminate or minimizereaction of iron and aluminum, asin the formation of intermetalliccompound between the two, alloying agents must generally be added to themolten aluminum bath, for example, silicon is often added. The presenceof the alloying agent, even in comparatively small amount, lowerselectrical conductivity of the resulting coating or film and also makesit less resistant to corrosion.

Bath or hot dip coating is difficult to conduct in a manner such thatuniform coating thicknesses are obtained, and particularly difficulty isencountered when thin coatings are attempted. Moreover, iron dissolvesfrom the wire (or other metal being coated) and contaminates the moltenaluminum.

The methods of coating a wire by electrophoretic deposition of powderedaluminum around the wire, followed by subsequent compaction, or by thecompaction of aluminum powder around a wire, both require relativelyexpensive powdered aluminum and are quite difficult processes tocontrol, for example, to control so that a predetermined coatingthickness having desired film characteristics is obtained. Preparationof thin films by these methods is particularly difficult.

It is known that certain metals form subhalides when placed in reactivecontact with vapor of a halide compound of the metal. For example, it isknown that liquefied metallic aluminum maybe reacted with aluminumtrichloride to produce aluminum monochloride. This reaction has beenused as a method of refining aluminum, however, as far as is known, ithas never been used for the deposition of thin films of pure aluminum onmetallic members, for example, thin films of pure aluminum on iron orsteel. It is believed that one reason the reaction has never beenadapted to a process for coating members of iron and steel is thedifficulty presented by formation of intermetallic compound between themetal of the body to be coated and the deposited aluminum. It would beexpected that the aluminum would enter into reaction, or alloy with, theiron from the underlying body. For example, in the case of coating ironand steel bodies, formation of undesirable intermetallic iron-aluminumcompound would ibe expected.

However, it has now been found, in accordance with the presentinvention, that aluminum, as well as certain other metals which would beexpected to cause difficulty by alloying the compounding with theunderlying body to be coated, may be deposited under certain conditionson a dissimilar metallic body by disproportionation of a subhalidecompound of the coating metal. Moreover, it has been found that this maybe accomplished in a manner by which thin films may be produced ofcontrolled thickness and a high degree of purity, with essentially nointermetallic compound being formed between the film metal and the metalsurface coated.

Accordingly, it is seen to be an object of the present invention toprovide a process for coating metallic surfaces with a film of adissimilar metal in such a manner that a high purity tilm is obtainedwhich is not alloyed with or otherwise compounded with the coated body.Moreover, it is an object to provide such a process which can beoperated to produce films of controlled and uniform thickness, includingquite thin films. It is a further object to provide such a process whichcan form a coa-ting of pure metal from scrap or comparatively impuremetal feed material. It is yet an additional object to provide such aprocess which can coat a continuously moving metallic member orsubstrate, for example, a wire or strip. It is yet an additional objectto provide comparatively simple yet eficient apparatus for practicingthe foregoing processes.

In accordance with the present invention, a vapor phase process isprovided for coating a metallic surface with a dissimilar metal film.The process comprises forming a subhalide vapor by reacting a metalhalide compound with elemental metal of the same kind as contained inthe metal halide compound, followed by contacting the subhalide vapor soproduced with the metallic surface to be coated while maintaining thetemperature of the metallic surface to be coated at a value below themelting point of the metal in the metal subhalide compound. Subhalidevapor decomposes, i.e. reacts by disproportionation, to deposit puremetal on the comparatively cold surface to be coated accompanied by theformation of metal halide vapor. The surface of the member to be coatedis maintained at a temperature above the condensation temperature of themetal halide to prevent deposition of the metal halide on the surface.

In a preferred embodiment, the metal to be deposited is aluminum and thesurface upon which it is to be deposited comprises a major proportion ofiron, e.g. iron, steel, etc.

In a specific preferred embodiment, the surface to be coated is thesurface of an iron or steel wire. The wire is continuously moved througha closed system in which the subhalide disproportionation reaction,accompanied by deposition of aluminum on the wire, takes place. Thespeed of the wire is regulated such that its temperature does not exceeda critical maximum of about 550 C. Before the Wire is moved into contactwith halide vapor, it is preferably raised to a temperature no lowerthan a value corresponding to the condensation temperature of aluminumtrichloride under the pressure which it exists in the system.

An important feature of the present invention is the effective totalre-cycle of the metal halide involved. The metal halide serves as atransfer or carrier means for elemental metal to be deposited, but thereis no net consumption of the metal halide in the processing reactions.Metal halide only need be supplied to make up for system losses.

The apparatus aspects of the present invention provide means for formingvapor of a metal halide compound, means for contacting the metal halidevapor with a source of elemental metal of the same kind as the metal ofthe metal halide compound in order to form subhalide vapor, and meansfor moving a metallic member into the presence of the subhalide vaporwhich was formed on the contact of the metal halide vapor and theelemental metal. The means for moving the metallic member are of such anature that the temperature of the metallic member is controlled whilethe member is in the presence of the subhalide vapor so thatdisproportionation of the subhalide vapor will occur in the vicinity ofthe member to deposit elemental metal from the subhalide vapor on themember, the elemental metal being deposited as a solid so that alloyingand intermetallic compound formation with metal from the member beingcoated is essentially eliminated.

In one preferred embodiment, a closed system is provided forsubatmospheric pressure deposition of the coating metal on the memberbeing coated. The system pressure is preferably maintained at betweenabout 2O and mm. of mercury. Partial pressure of subhalide vaporpreferably ranges from about 10%-25% of the system pressure. One aspectof this embodiment provides apparatus adapted to permit diffusion ofmetal halide vapor being formed on disproportionation so that fullre-cycle of aluminum trichloride is effectively provided.

In another embodiment, a full tiow system is provided for the depositionof metal on a dissimilar metallic surface being passed through thesystem. This embodiment includes a liquid metal-to-vapor contact vesselwherein a metal halide-rich vapor stream contacts a liquid metal of thesame type contained in the metal halide to produce metal subhalidevapor. The metal subhalide vapor so produced changes the streamcomposition to cause it to be metal subhalide-enriched. A heated coatingchamber is provided which receives the subhalide enriched vapor. Meansare provided for moving a member to be coated through the coatingchamber at a predetermined rate such that its temperature does notexceed tthe melting point of tthe metal being deposited. Means areprovided for returning metal halide-enriched vapor to the contact vesselafter disproportionation of the subhalide-enriched vapor to depositmetal on a metal surface being coated has occurred within the coatingchamber. Preferably, the heating means for the system insure that themember being coated is at a minimum temperature no less than thecondensation temperature of the metal halide, prior to contact of themember with any vapor containing metal halide.

For a more complete understanding of the present invention and forfurther objects and advantages thereof, reference may now be had to thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIGURE 1 is an elevational sectional view of apparatus for coating awire in accordance with the present invention; and

FIGURE 2 is a schematic, flow diagram illustrating a full ow process forpractice of the present invention, and illustrating certain apparatusutilizable in such process.

Turning now to FIGURE 1, therein is shown a closed reactor system,indicated generally by the numeral 11. Reactor system 11 may be utilizedto coat metallic members with a thin layer of metal; specifically tocoat a wire, eg. iron or steel, with a thin layer of metal, e.g.aluminum.

The reactor system 11 includes the annular quartz outer reactor casing13 and the oppositely disposed reactor closure fittings 15 and 17.Closure fittings 15 and 17 may be made, for example, of brass. Fittings15 and 17 each include an enlarged disk 18 which serves as a respectiveend wall or head for the opposite ends of the outer reactor casing 13.The disks 18 are held tightly in position against the casing ends, as byC-type clamps 19, which engage edge portions of a disk and a respectiveshoulder formed on each casing end by enlarged diametrical casing endportions 21 and 23. O-rings (not illustrated), or other conventionalseal elements, are provided to insure a tight seal. Closure fittings 15and 17 each carry outwardly projecting Vacuum staged wire guideassemblies 27. Each assembly 27 is generally of cylindricalconfiguration and formed with a coaxially disposed array of apertures inits structure in alignment with aperture 29 in the disk portion 18 ofthe closure fitting. A plurality of axiallyaligned spaced-apart guiderings 31 are carried within successive annular compartments 32 which areformed within the body of each wire guide assembly 27. The alignedcentral openings in guide rings 31 and the coaxially-disposed aperturesin each wire guide assembly permit wire to pass through the assembly andits corresponding aperture 29 in closure disks 18.

Various materials of construction may be used for the formation of theguide rings 31, an example being alumina.

Nipples 33, 35, 37 and 38 extend from the sides of each wire guideassembly 27 and respectively communicate with spaced-apart coaxialcavity regions 39 formed in the body of each fitting 27.

Outer reactor casing 13 is provided with a pair of nipples 40, whichpermit communication wtih the interior of the casing.

A reactor chamber 41 is contained within the interior of outer reactorcasing 13. Reactor chamber 41 may be of any desired shape, for example,cylindrical, and it `may be made of various materials, for example,graphite. Conduit means 43, formed in the outer casing 13, extends fromchamber 41 downwardly to supply vessel `45 and permits communicationbetween the interior of reactor chamber 41 and the interior of thesupply vessel 45. Conduit means 43 is tted with a valve 47 which Imay beadjusted as desired, but which is normally open during operation. Aconduit 51 leads into a lower side portion of vessel 45. A valve means53 is provided for conduit 51.

Vessel 45 is submerged in the heat transfer fluid 57, which is containedwithin heat transfer uid tank 59. The heat transfer fluid 57 may be keptat a controlled temperature by means of resistance heater 61, which hasits power input controlled by a rheostat 63. The heat transfer uidtemperature is sensed by the thermocouple 65, which is disposed tocontact the heat transfer liquid 57. The output from thermocouple 65leads to temperature controller 67, the output of which controls thepower to maintain a desired predetermined temperature for heat transferfluid 57.

Heating means are provided to maintain the conduit 43 at a constanttemperature somewhat above the temperature of heat transfer iluid 57.'Resistance heating tape may be wrapped about the conduit and suppliedwith power to accomplish this purpose, or various other conventionalheating means may be used. In FIGURE 1, the heating means areschematically represented as resistance heater 69. Conventional controlmeans (not illustrated) control the power to resistance heater 69 tomaintain the conduit 43 at the desired predetermined temperature.

RF heating is provided for graphite reaction chamber 41 by means of RFcoil 75, which is disposed about the outer regions of casing 13,adjacent the proximity of graphite reactor chamber 41. The .RF powersource 77 is controlled by power controller means 79, the output ofwhich is dependent upon the output of thermocouple 80, which is xed inthe walls of graphite chamber 41. It can thus be seen that power to RFcoil 75 is controlled to maintain the temperature of the reactor chamber41 at a desired predetermined value.

A dish 81 rests on the oor of reaction chamber 41. It may be made ofvarious materials, for example, alumina.

Wire supply spool 82 and wire take-up spool 83 are rotatably mounted atopposite ends of the closed reactor system 11. Wire 85 passes fromsupply spool 82 via the wire apertures of wire guide assembly 27 offitting 15 into the interior of casing 13 and enters the reactorcharnber 41 through a close tting chamber wall aperture 87 and exitsfrom the chamber 41 through a close fitting aperture 89 in an oppositelydisposed wall region to emerge in the interior portion of casing 13adjacent tting 17. Thereafter, the wire 85 emerges from the assembly 11by passing through the wire guide 27 of closure fitting 17, and is takenup on spool 83.

An example of the operation of the apparatus of FIGURE 1 will now begiven. The vessel 45 is loaded with aluminum trichloride, represented bythe numeral 90 in FIGURE 1. The dish 81 in reactor chamber 41 is filledwith aluminum 91. The valve 47 i-s Placed in an open position. The valve53 is in the closed position. The RF heating coil 75 is activated bysupplying power from power source 77. Vacuum pumps, schematicallyillustrated by arrows 92, 93, 95, and 97 are connected to nipples 35,37, 3S and 40, respectively, and activated to evacuate the chamber 41and the interior of casing 13. Note that a staged vacuum pump-sealconfiguration is thus provided to maintain desired low pressures withinthe system while permitting wire to enter and leave the low pressureinterior of the system. Argon, helium, or other inert gas from asuitable supply, schematically illustrated by arrows 99, is continuouslypassed through the wire guide assemblies 27 via nipples 33. For the mostpart this inert gas is exhausted by the various vacuum pumps. Itspresence provides an inert atmosphere for the low pressure interior ofcasing 13.

A pressure of from about 20 to 100 mm. of mercury, preferably 2() to 40mm. of mercury, is established and maintained within the interior ofcasing 13. The heat transfer uid 57 is raised to and maintained at atemperature of no less than about 100 C., preferably about 135 C. The RFheating coil 75 is activated and the controls set so that thetemperature within reactor chamber 41 is in excess of 700-800 C.,preferably about 1025 C., and no greater than about 1250 C. Thetemperature of conduit 51 is maintained by resistance heater 69 at over100 C., preferably at about 140 C.

Aluminum trichloride is vaporized and enters the reactor chamber 41. Aslightly higher pressure exists within reactor chamber 41 than withinthe regions in casing 13 which surround chamber 41. A small leakage ofgas from the chamber outwardly into the cylinder accordingly occursthrough the clearances of the apertures S7 and 39.

The aluminum 91 in dish S1 is in the liquid state in view of the hightemperature that prevails in reactor chamber 41. Aluminum trichloridegas in chamber 41 contacts the liqueiied aluminum and reacts with it inaccordance with the following reaction:

Thus, it is seen that aluminum monochloride is formed. The aluminummonochloride so formed is gaseous. It transfers by diffusion from theregion of its formation to the wire 35, which is being pulled throughthe reactor chamber 41 by means of the take-up reel 83.

When the aluminum monochloride strikes the comparatively cold wire,disproportionation of the aluminum monochloride occurs as follows:

Thus, it is seen that the aluminum monochloride decomposes into aluminumtrichloride and aluminum. The aluminum is deposited upon the cold wire.The speed of the wire is maintained such that its temperature lies belowthe melting point of aluminum. Accordingly, a solid film of high purityaluminum is deposited upon the wire. Essentially no alloying orintermetallic compounding occurs 'between the aluminum and the wire.

The configuration of the reactor system 11, including its heating means(RF coil 75) is such that wire, maintained at the proper speed, entersreactor chamber 41 after the wire has reached a temperature in excess ofthe condensation temperature of aluminum trichloride under the pressureconditions of the system. This prevents deposition of aluminumtrichloride on the wire. Preferably, the initial temperature of the wireentering the reactor chamber 41 is no less than about 200 C.

The wire speed for a graphite reactor chamber temperature of about 1025C. may vary from on the order of about one foot per minute to on theorder of about feet per minute, with from about 10-60 feet per minutebeing the preferred speed range.

The aluminum trichloride formed at the wire upon disproportionation ofthe aluminum monochloride diffuses into the atmosphere prevailing in thereactor chamber 41, and in time again contacts the liquefied aluminum 91in dish 81 to form more aluminum monochloride for disproportionationreaction at the wire. Thus, effectively, a re-cycle of aluminumtrichloride is provided. Note that no aluminum trichloride whatsoever isconsumed in the reaction. The consumption of aluminum trichloride supply90 is limited to the make-up of aluminum trichloride losses through thevacuum system described.

The concentration of the aluminum monochloride vapor in the reactorchamber 41 is such that it has a partial pressure which is about 10%-25%of the total pressure prevalent in the chamber, the balance beingattributable to a major proportion of aluminum trichloride vapor and aminor proportion of inert gas.

In another method of operation, valve 53 is opened and hydrogen gas orother carrier gas is permitted to flow through conduit 51 into vessel45. The hydrogen produces a driving or carrier means to assist incarrying aluminum trichloride into the vicinity of liquid aluminum 91 indish 81. While a considerable amount of loss is experienced by the modeof operation involving hydrogen flow (flow established through wireclearance of apertures 87 and 89), some advantage is gained in speedingup the contact of aluminum trichloride for reaction with aluminum toform the monochloride.

FIGURE 2 illustrates a somewhat modified system for coating wire withmetal in accordance with the present invention. Therein, a furnace 101is disposed intermediate wire feed reel 103 and wire take-up reel 105.Wire 107 pass from the feed reel 103 through a wire inlet passage in onewall of furnace 101 and exits through an outlet passage in an oppositewall to wind on the take-up reel 105. The cylindrical contact vessel 109preferably has its interior packed with particles of aluminum, or thelike. A feed line 111 communicates with the upper side portion of thevessel 109 and a discharge line 113 leads from the bottom. Liquidaluminum input enters from an aluminum make-up source, schematicallyillustrated by an arrow 115, via valve 117 to join fiuid flowing in line113. Line 113 leads to the pump 119, which pumps the fluid via heatexchanger 121 to contact feed line 111. Liquid aluminum flows downwardlyin the contact vessel 109 to countercurrently contact aluminumtrichloriderich gas passing upwardly in the vessel. Aluminummonochloride is formed by the reaction between the hot liquid aluminumand aluminum trichloride-rich gas. Aluminum monochloride so formed inthe column provides an aluminum monochloride-enriched gas at the top ofthe column. This aluminum monochloride-enriched gas flows throughconduit 123 to enter the furnace 101, where it contacts thecomparatively cold wire 107. Disproportionation of the aluminummonochloride results and aluminum is deposited on the wiresimultaneously with formation of aluminum trichloride gas. The aluminumtrichloride gas is returned to the bottom of the column 109 by means ofline 12S. In establishing operation for the system of FIGURE 2, itshould be appreciated that aluminum trichloride vapor must be introducedinto the system, for example, via the inlet line 127 from an externalsupply, schematically illustrated by arrow 128. In operation, the valve130 in line 127 is adjusted to admit additional aluminum trichloride tocompensate for system losses.

In the system of FIGURE 2, it is sometimes found desirable to introducea quantity of gas which is inert relative to the reactions andconstituents involved, e.g. hydrogen, argon, helium, etc. may be used.The gas can be introduced continuously at a comparatively slow rate orit may be injected at intervals, as desired. The inert gas may beintroduced at various locations in the system, for example, into thebottom of column 109 along with the aluminum trichloride-rich gasflowing in line 125.

Temperature of the furnace 101 is maintained at over 700-800 C.,desirably at about 1025o C., but no greater than about l025 C. Wirespeed is maintained so that maximum wire temperature remains well belowthe melting point of aluminum during its passage through the furnace101. Moreover, the speed is maintained, such that wire is above thecondensation temperature of aluminum trichloride before it enters afurnace region where the aluminum trichloride-aluminum monochloride gasmixture is present. Generally, the heat conductivity of the wire permitssufficient heat transfer along it to insure that the entering wiretemperature is sufiicient, but if required for certain system geometryor at high wire speeds, a preheater may be provided for the 107 beforeit enters the furnace.

Preferably the furnace 101, which provides, in effect, heated coatingchamber means, is operated so that an inert environment is provided forcontact of wire 107 and subhalide vapor. Thus, an internal chamber, withappropriate wire guide fittings (such as wire guide assemblies 27 ofFIGURE l) may be used, with heat applied to the exterior of the chamberby various means, e.g. electrical heating, heat transfer from hot gases,etc.

The thickness of coating deposited on a wire-like member, in accordancewith the present invention, may vary over a wide range. For example, acoating or film of about l to 2 microns thickness may be deposited on asteel wire of '0.40 inch diameter by use of the apparatus of FIGURE l,with a wire speed of about 25 feet per minute and a reactor chambertemperature of approximately 1025o C. If the speed is decreased to about5 feet per minute, the thickness of the coating is about 4 to 6 microns.Thicker and thinner films may be obtained by varying speeds and otherconditions. If desired, a wire may be passed through the present processfor several runs, to make a film as thick as wanted.

While it is preferred that members coated in accordance with the presentinvention comprise a major proportion of iron (eg. iron, steel, highcarbon steel, stainless steel wire, etc.), various other metals andalloys may serve as the material of construction for a member to becoated. Examples of such materials are copper, tantalum, tungsten,niobium, molybdenum, nickel, platinum, palladium, silver, gold,titanium, chromium and mixtures and alloys thereof.

Films of metals other than aluminum may be deposited in accordance withthe present invention. For example, titanium, chromium, nickel,manganese, germanium and cobalt films or coatings may be deposited bydisproportionation of the subhalide of such metals.

While the chloride is preferred for practice of the present invention,other halides are applicable. For example, aluminum tribromide, aluminumtriiodide, and aluminum trifluoride may be used in place of aluminumtrichloride.

The term wire like, as used herein, is intended to refer to an elongatedmember such as a wire, strip, rod, etc.

What is claimed is:

1. A process for continuously coating a wire-like mernber comprising amajor proportion of iron with an aluminum film comprising:

(a) forming aluminum monochloride by reacting aluminum trichloride vaporwith elemental liquid aluminum at a temperature no less than about 700C., and passing said aluminum monochloride into a reactor chambermaintained at a temperature of at least 700 C.,

(b) moving said wire-like member through said reactor chamber containingsaid aluminum monochloride7 said wire-like member having a temperaturegreater than 200 C. and being moved through said chamber at a rate suchthat the temperature of said wire-like member does not exceed a criticalmaximum temperature of 550 C., said rate ranging between about l andfeet per minute,

(c) effecting disproportionation of said aluminum monochloride todeposit aluminum on said wire-like member and liberate aluminumtrichloride to effect an aluminum trichloride-rich atomsphere.

(d) recycling said aluminum trichloride-rich atmos- 9 10 phere intocontact with said elemental liquid alu- 2,711,973 6/ 1955 Wainer et al.117-107.2 mnum in accordance with step (a). 2,731,361 1/1956 Nack et al.117-107 .2 X 2. The method of claim 1 in which the pressure in said2,856,312 10/1958 Nowak et al. 117-1072 X pressure in said reactorchamber is maintained at no 2,887,407 5/ 1959 Koch 117-107.2 greaterthan about 100 mm. of mercury. 5 2,930,347 3/1960 Bnllol 117-107.1 X 3.The method of claim 1 in which a carrier lgas lis 3,096,209 7/ 1963Ingham 117-107.2 X employed in a system to carry said aluminum mono2,898,230 8/1959 Bulloi 117-107.2 chloride into said reactor chamber.

4. The method of claim 3 in which the partial pressure OTIIER RFFERENESof aluminum monochloride in said system is maintained 10 Powell et al-ValPl Plating, Published by John Wiley at about 5%-25% of the systempressure. & SOUS 1955 TS695B3, PP- 3, 4, 9 t0 11, 25, 26 and 29References Cited relied upon' UNITED STATES PATENTS ANDREW G. GOLIAN,Primary Examiner 1,770,177 7/ 1930 Martin. 15 US. C1. X.R. 2,344,138 3/1944 Drummond ll7-107.1

2,384,500 9/1945 Stoll -..-2 11S-49.1 X 117-107'1 107'2

